Slow breathing and heart rate variability: what actually happens in your body

Author: Raymond Hackland · Last reviewed: 18 October 2026 · Reading time: about 6 minutes

In short

• What this is: Your heart does not beat like a metronome. The small changes from one beat to the next are called heart rate variability (HRV), and part of that variation follows your breath.
• What the evidence says: Hundreds of studies, pooled in a 2022 meta-analysis of 223 studies, found that slowing your breathing, often to about six breaths a minute, increases the part of HRV linked to the vagus nerve, both during practice and afterwards.
• What it means for your practice: Slow, unhurried breathing measurably changes how your heart and breath work together. This is physiology, not a treatment for any condition, and you don’t need a device to breathe slowly.

Background

This paragraph describes tradition, not science. Slow breathing is at the heart of many contemplative practices. In the Chinese Qigong tradition, the breathing of Liu Zi Jue, the Six Healing Sounds, is described as in through the nose and out through the mouth, “even, fine, soft and long” [6]. These instructions are centuries older than any heart-rate monitor. The research below is a modern, separate line of enquiry, but it helps explain what happens in the body when breathing slows down.

What science says

Your heartbeat follows your breath. When you breathe in, your heart speeds up slightly; when you breathe out, it slows down again. This rhythm is called respiratory sinus arrhythmia (RSA), and it is one of the main components of HRV [1, 4]. Most people, most of the time, breathe about 9 to 24 times a minute [1].

What changes at about six breaths a minute. Paul Lehrer and Richard Gevirtz, two researchers in heart rate variability biofeedback, summarise decades of work: the heart-rate swings that come with each breath become largest when people breathe at about 0.1 Hz, that is, about six breaths a minute, or one breath every ten seconds [1]. At this pace, heart rate and breathing rise and fall exactly in step.

The usual explanation involves the baroreflex, a fast feedback loop that keeps blood pressure steady. Pressure sensors in the large arteries report to the brainstem, which adjusts the heart rate. Because the loop has a built-in delay, it has a natural rhythm of its own, close to 0.1 Hz. Breathing at that rhythm drives the loop at just the right pace, and the swings grow [1]. In physics, this is called resonance, which is why the method is known as “resonance frequency breathing”. The best pace differs slightly from person to person. Lehrer’s group found an average of about 5.5 breaths a minute, with somewhat lower frequencies in taller people and in men [1].

What the reviews find. A 2018 systematic review included 15 studies of slow breathing (under 10 breaths a minute) in healthy people. Slow breathing increased HRV and RSA and was accompanied by changes in brain activity on EEG. Participants also reported feeling more relaxed and comfortable, and less anxious [2]. The largest review so far, a 2022 meta-analysis of 223 studies, found that the vagally mediated part of HRV rose during slow breathing, straight after a single session, and after programmes of several sessions [3]. A 2017 educational review in the journal Breathe describes further documented effects in healthy people, including more efficient ventilation, higher baroreflex sensitivity and closer coupling between heart and lungs [4]. Lehrer and Gevirtz also report that baroreflex gain rose markedly during biofeedback sessions, and that after about three months of twice-daily home practice it was higher at rest as well [1].

Breathing out on a sound. In a 2001 study, 23 healthy adults recited the Ave Maria in Latin or a yoga mantra. Both slowed breathing to about six breaths a minute. Cardiovascular rhythms became stronger and synchronised, and baroreflex sensitivity rose on average from 9.5 to 11.5 ms/mmHg [5]. This was one small study, but it shows that rhythmic, voiced exhalation can bring people into this slow range almost by itself.

How strong is this evidence? The basic physiology has been found consistently in a large number of studies, which is why this article carries the Well studied label. Two limits matter. First, many individual studies were small, and the 2022 meta-analysis pooled very different methods. Second, HRV is a measurement, not a health outcome. These findings describe what happens in the body; on their own, they do not show that slow breathing prevents any illness or works as a medical treatment.

Where popular claims go beyond the evidence

• “Raise your HRV and you fix your health.” HRV is often used as a marker of physical and emotional resilience [1]. Raising it during a breathing session is not the same as changing the course of a disease. HRV biofeedback is studied in clinical research, but that research is separate from everyday self-practice, and it is not a reason to replace medical care.
• “Six breaths a minute is a magic number.” It is an average. The pace at which the swings peak differs between people [1]. Breathing a little slower than usual, without strain, matters more than hitting exactly 6.0.
• “The longer the exhale, the better.” Long exhalations can feel calming. However, the Breathe review reports that studies found a tendency for baroreflex sensitivity and HRV to increase most with equal in- and out-breaths during slow breathing at 0.1 Hz [4]. A few small studies suggest that a slightly longer out-breath may add a little to some HRV measures, but the results are mixed, as we explain in Long exhalation and the vagus nerve.
• “Slow breathing switches on your vagus nerve and calms inflammation.” That goes well beyond what the studies cited here measured. We look at the vagus nerve, what’s known and what’s hype, in Long exhalation and the vagus nerve.

How this relates to the Six Healing Sounds, Qigong and neigong

Label for this section: Well studied (slow-breathing physiology) · Tradition only (Qigong and neigong concepts).

Each of the six sounds is carried on a long, unhurried exhalation, followed by a quiet in-breath through the nose. When the sounds are practised slowly, a full breath can take several seconds, so a session may well come close to the slow range described above. Whether it does depends on your own pace, and the studies cited here did not test Liu Zi Jue itself. The rosary-and-mantra study [5] suggests that voicing a sound on the out-breath is one natural way to slow down. Whether making the out-breath longer than the in-breath adds anything beyond slowing down is not settled; we look at that question in Long exhalation and the vagus nerve.

Qigong and neigong describe breathing in their own terms: “even, fine, soft and long” [6], with attention gathered inwards and talk of qi. Where the word Qigong itself comes from is explained in our introduction to Qigong. These are traditional descriptions, not physiology, and they are worth knowing on their own terms. The overlap with HRV research is real in one narrow sense: both involve slow breathing. But “cultivating qi” and “raising HRV” are not the same claim, and none of the research cited here measured qi.

Resonance Heritage Qi is a personal, music-assisted practice inspired by Liu Zi Jue: connected to it, not a replacement for the traditional form or for study with a teacher of that tradition. If you want to explore the slow breathing described here, the sounds give you a gentle, structured way to do it, without needing to count or watch a screen.

Try it gently (optional)

1. Sit upright and comfortably. Let your shoulders drop.
2. Breathe in quietly through your nose for about five seconds.
3. Breathe out softly for about five seconds, through the nose or on a whispered “hhh” through the mouth.
4. Continue for three to five minutes. If counting makes you tense, simply breathe a little slower than usual.
5. Finish with a few natural breaths and notice how you feel.

Never force your breath. If you feel dizzy, lightheaded or short of breath, stop and breathe normally.

Sources

1. Lehrer PM, Gevirtz R, 2014. Heart rate variability biofeedback: how and why does it work? Frontiers in Psychology 5:756. https://doi.org/10.3389/fpsyg.2014.00756
2. Zaccaro A, Piarulli A, Laurino M, Garbella E, Menicucci D, Neri B, Gemignani A, 2018. How breath-control can change your life: a systematic review on psycho-physiological correlates of slow breathing. Frontiers in Human Neuroscience 12:353. https://doi.org/10.3389/fnhum.2018.00353
3. Laborde S, Allen MS, Borges U, Dosseville F, Hosang TJ, Iskra M, Mosley E, Salvotti C, Spolverato L, Zammit N, Javelle F, 2022. Effects of voluntary slow breathing on heart rate and heart rate variability: a systematic review and a meta-analysis. Neuroscience & Biobehavioral Reviews 138:104711. https://doi.org/10.1016/j.neubiorev.2022.104711
4. Russo MA, Santarelli DM, O’Rourke D, 2017. The physiological effects of slow breathing in the healthy human. Breathe 13(4):298–309. https://doi.org/10.1183/20734735.009817
5. Bernardi L, Sleight P, Bandinelli G, Cencetti S, Fattorini L, Wdowczyc-Szulc J, Lagi A, 2001. Effect of rosary prayer and yoga mantras on autonomic cardiovascular rhythms: comparative study. BMJ 323(7327):1446–1449. https://doi.org/10.1136/bmj.323.7327.1446
6. Chinese Health Qigong Association, 2016. 健身气功·六字诀功法源流 (Health Qigong Liu Zi Jue: origins of the method). Health Qigong Management Center, General Administration of Sport of China, published 20 December 2016. https://www.sport.gov.cn/qgzx/n5407/c781291/content.html

Source quality note: Sources [1] to [4] are reviews; [3] is the largest meta-analysis to date (223 studies), and [2] covers healthy people only. [1] is a narrative review written by researchers who developed the biofeedback method. [5] is a single small study (23 people). The physiology is consistent across studies, but most individual trials are small and they measure heart and breathing signals, not health outcomes. Source [6] is a traditional description of the breathing method, not a scientific source.